Preparation Of Efficient Adsorbent Based On Multicomponent Reactions And Its Environmental Application Study

For the past few years,nanomaterials have exhibited broad application in environmental pollution adsorption due to their extraordinary properties.However,most of these pristine nanomaterials still suffer from some drawbacks such as limited adsorption capacity and poor dispersibility in water.In this thesis,we developed a facile and mild route for the preparation of new high-efficiency adsorbents via multicomponent reactions.In this study,magnesium/aluminum layered double hydroxides（LDH）and multi-walled carbon nanotubes（MCNTs）were used as the matrix materials,and Kabachnik-Fields tri-component reaction and MALI tri-component reaction were selected as surface functionalization methods.Diethyl phosphite,chitosan and styrene sodium sulfonate polymeric polymers were used as decorations to prepare LDH-PDA-DEP,CNTs-CHO-CS and CNTs-CHO-PSPSH composites,respectively.The morphology,surface functional groups and chemical compositions of the as-prepared samples were characterized by EDS,TEM,XPS,FT-IR,and TGA.The adsorption experiments（adsorption time,solution pH,initial pollutant concentration and solution temperature）were conducted under different conditions with Cu²⁺and methylene blue as pollutant models.Additionally,the adsorption isotherms,kinetics,and thermodynamics of the adsorption process were discussed further.The main results show that:1)LDH-PDA-DEP composites were prepared successfully by Kabachnik-Fields tri-component reaction between amino functional groups generated by the oxidative self-polymerization of dopamine on the surface of LDH,benzaldehyde,diethyl phosphite,and thiourea.The results demonstrated that the LDH-PDA-DEP composites showed a significantimprovementintheadsorptionefficiencytowardsCu²⁺.Along with the increase of the solution pH,the removal amount of Cu²⁺increased gradually.Kinetics study revealed that the experimental data fitted well with the pseudo-second-order model.Adsorption isotherms showed that the Langmuir isotherm model can provide a better description of experimental equilibrium adsorption data,with the maximum monolayer adsorption capacity of 105.44 mg/g.Thermodynamic parameters indicated that the adsorption of Cu²⁺by LDH-PDA-DEP was a spontaneous and endothermic process.2)The carbon nanotubes modified with styrene sodium sulfonate polymer were successfully prepared by Kabachnik-Fields reaction between carbon nanotubes,furfural,diethyl phosphite,and amino-functionalized sodium styrene sulfonate.Adsorption experiments indicated that the adsorption equilibrium can be achieved within 20 min.The equilibrium adsorption capacity of MB by CNTs-CHO-PSPSH reached up to 178.57 mg/g,which was about 4.7 times higher than that of the unmodified CNTs（37.73 mg/g）.The adsorption capacities of modified CNTs increased with the increase in pH.The adsorption isotherms data were preferably fitted to the Langmuir model,yielding the maximum adsorption capacity of 346.88 mg/g at 298 K.Thermodynamic studies indicated that the adsorption was an exothermic and physical process.The possible mechanisms of adsorption may be attributable toπ-πstacking or electrostatic interaction.3)The chitosan-coated carbon nanotube composites were fabricated via a MALI tri-component reaction under rather mild conditions,in which mercaptoacetic acid serves as a“lock”.Adsorption processes were fitted well by the pseudo-second-order kinetic model.Equilibrium data could be best described by Langmuir isotherm model,signifying a monolayer adsorption process.The maximum absorption capacity was calculated as 115.84mg/g.Thermodynamic studies indicated that the adsorption of Cu²⁺onto the CNTs-CHO-CS composites was an endothermic and spontaneous process,which demonstrated that the adsorption is more favorable at a higher temperature.Moreover,the adsorption of Cu²⁺onto CNTs-CHO-CS also be affected by solution pH significantly.The highest adsorption capacity was observed at pH 8.